Interference of electronic circuitry caused by electromagnetic radiation is a known problem. In the case of SIM cards, the interference may be from low frequency base-band noise (e.g. of the order or several hundred kHz) or RF feeding (e.g. of the order to thousands of MHz) from the antenna back to the handset. Shielding of SIM cards to reduce the effect of such radiation is known e.g. GB2269940.
Filters are often used in electronic memory card connectors to prevent interference from affecting correct operation of the electronic memory cards, and the electronic devices to which they are connected. FIG. 1 shows an Application Specific Integrated Parts (ASIP) filter 101 provided in such a capacity for a SIM card connector 100, positioned on the surface of a printed circuit board 102. The ASIP filter 101 is connected, via tracks 103 (only some shown) to each of the SIM card connector contacts 104. This provides filtering to each of the SIM card connector contacts, and thus in turn to the SIM card (not shown).
The tracks 103 connecting the filter 101 to each of the SIM card contacts 104 act as antennae, particularly at high frequencies (1-2 GHz typical cellular radio operating frequency). This can cause noise to be present in the tracks which, via the SIM card contact pins 104, may affect the operation of the SIM card. As SIM card operating voltages reduce, increasingly smaller amounts of noise can be found to affect performance. This is because the noise represents a bigger proportion of the overall signal.
The SIM connector pins 104 may also pick up noise as they also can act like antennae. If this noise is not filtered then the noise will penetrate inside the phone and may cause the IC inside the phone to fail. Also, Electrostatic Discharge (ESD) can penetrate inside the phone and may cause failure of the phone IC.